Final answer:
In the MF band, the correct frequency for Digital Selective Calling (DSC) is A. 2187.5 kHz, which is used for distress and safety calls in maritime communication.
Step-by-step explanation:
In the MF band, the correct Digital Selective Calling (DSC) frequency is A. 2187.5 kHz. Frequency is a fundamental concept in physics related to the number of cycles of a periodic wave that occur per unit of time, and it is typically measured in hertz (Hz). In the context of communication systems, such as Maritime Mobile Service, the MF band is utilized for medium-distance communication and has designated frequencies for various purposes including emergencies and DSC.
The frequency 2187.5 kHz is specifically allocated for DSC distress and safety calls in the medium frequency (MF) maritime band. Other listed options, B. 156.525 MHz, C. 243.0 MHz, and D. 121.5 MHz, correspond to other communications purposes in VHF (very high frequency) and UHF (ultra high frequency) bands.